Characterization and Fuel Cell Testing of Radiation-Grafted Psi Membranes

Abstract

We have demonstrated earlier the useful performance of our PSI radiation-grafted membranes in terms of the current-voltage characteristics of 30 cm2 active area fuel cells containing these membranes and their long-term testing over 6,000 h at 60 °C. We report here on testing of PSI radiation-grafted membranes in these fuel cells at 80 °C and in short stacks comprised of two or four 100 cm2 active area cells. The in-situ degradation of membranes has been investigated by characterizing membranes both before testing in fuel cells and post-mortem after testing in fuel cells. Characterization was accomplished by means of ion-exchange capacity and infrared and Raman spectroscopic measurements. In addition, a rapid screening method for our ex-situ testing of the oxidative stability of proton-conducting membranes was developed in this work. Comparison of the initial screening test results concerning the oxidative stability of some perfluorinated, partially-fluorinated, and non-fluorinated membranes compare well qualitatively with the relative stability of these same membranes during their long-term testing in fuel cells.

Effect of crosslinkers on the preparation and properties of ETFE‐based radiation‐grafted polymer electrolyte membranes

“…Among these membranes being developed, radiation-grafted membranes have become attractive materials because of their high proton conductivity and relatively lower cost. The longest durability of the PEMFC with the radiation-grafted membranes has reported to be 10,000 h, 3 and the price of the radiation-grafted membranes is considerably lower than that of the commercial perfluorosulfonic membranes. In addition, the radiation-grafted membranes have also been used in electrodialysis, elec-trosynthesis, protein extraction, and purification and recovery in etching processes.…”

2,3,7,8‐tetrachlorodibenzo‐p‐dioxin (TCDD) inhibition of coronary vasculogenesis is mediated, in part, by reduced responsiveness to endogenous angiogenic stimuli, including vascular endothelial growth factor A (VEGF‐A)

“…The accelerated testing of the oxidative stability of candidate membranes can be carried out by exposure to hydrogen peroxide solutions containing redox active species. In a previous work,7 we showed a qualitative correlation between the retention of membrane properties in such accelerated tests and the membrane lifetime and stability in PEFCs.…”

“…Some films were preirradiated in air with a 60 Co γ‐irradiation source; others were preirradiated in an air or nitrogen atmosphere with an electron‐beam source. We optimized several parameters in our irradiation conditions earlier to achieve a maximum grafting yield by minimizing radical consumption through combination or degradation reactions 4, 5, 7, 16. For example, samples were cooled by being placed on dry ice during radiation processing, and thermally sensitive colorimetric indicator strips confirmed that the macroscopic temperature of the samples remained subambient.…”

“…The membrane properties were characterized with our earlier reported methods 4–7. The ion‐exchange capacities (IECs) of the FEP25 membranes were between 1.25 and 1.35 mequiv/g, the water swelling was between about 15 and 20 mass %, and the swollen membrane thickness was about 35–40 μm.…”

“…Since this earlier work with FEP, interest in radiation‐grafted membranes for fuels cells has shifted to partially fluorinated polymers such as ETFE (ethylene‐tetrafluoroethylene copolymer or poly(ethylene‐ alt ‐tetrafluoroethylene)) to improve mechanical properties and to poly(vinylidene fluoride) (PVDF) 4, 7, 12. In addition, the emphasis has increasingly changed to faster, safer, easier to use, and more environmentally friendly electron‐beam sources.…”